The present invention relates to an energy-efficient automobile adapted to reduce a motive-power generation amount of a prime mover, in a traveling environment or an operating condition where a motive power required for traveling is less than a motive power corresponding to an amount of depression of an accelerator pedal.
Generally, in an automobile, a motive power to be generated by a prime mover is controlled by manipulating an accelerator pedal. For example, in an automobile equipped with a spark-ignition engine having an electronically-controlled throttle valve, a target opening angle of the throttle valve corresponding to an amount of depression of an accelerator pedal detected by an accelerator pedal sensor (the amount will hereinafter be referred to as “accelerator-pedal depression amount”) is calculated, and a control signal corresponding to the calculated target opening angle is output to an actuator of the throttle valve to control an opening angle of the throttle valve and eventually control a motive power to be generated by the engine (see, for example, JP 2001-280180A).
In an automobile equipped with a diesel engine having an electronically-controlled injector, a target fuel injection amount of the injector corresponding to an accelerator-pedal depression amount is calculated, and a control signal corresponding to the calculated target fuel injection amount is output to the injector to control a fuel injection amount of the injector and eventually control a motive power to be generated by the engine (see, for example, JP 2007-064191A). In an electric automobile equipped with an electric motor as a prime mover, an electricity corresponding to an accelerator-pedal depression amount is supplied to the electric motor to control a motive power to be generated by the electric motor (see, for example, JP 2002-199513A).
As above, in an automobile equipped with a prime mover, such as a spark-ignition engine, a diesel engine or an electric motor, a motive power conforming to driver's intention is output from the prime mover, according to an accelerator-pedal depression amount. However, depending on a traveling environment or an operating condition, it is not always necessary to output a motive power corresponding to an accelerator-pedal depression amount during operation of the automobile.
For example, when the automobile is traveling on a road surface having a relatively steep downward slope, or when a relatively strong tail wind is blowing to the automobile being traveling, an external force is applied to the automobile in a forward traveling direction thereof, and thereby the motive power of the prime mover becomes excessive by just as much as the external force. Thus, the conventional automobile has a problem that fuel or energy is uselessly consumed in a situation where a required motive power is less than a motive power corresponding to an accelerator-pedal depression amount, resulting in deterioration in energy efficiency thereof.